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..The... 


Quantitative  Determination 

of 

Boric  Acid 

in 

Tourmaline 


THESIS 

Presented  to  the  Faculty  of  the  Department  of  Philosophy 
of  the  University  of  Pennsylvania,  for  the 
Degree  of  Doctor  of  Philosophy 


BY 

GEORGE  WILLIAM  SARGENT 

BELLWOOD,  PA. 


PHILADELPHIA 
AVIL  PRINTING  COMPANY 

1898 


This  investigation  was  undertaken  at  the  suggestion  of 
Professor  Edgar  F.  Smith,  and  I take  this  opportunity  of 
sincerely  thanking  him  for  his  encouragement  and  ready 
advice  throughout  the  work. 


INTRODUCTION. 


Nothing  of  the  constitution  of  this  mineral  is  understood. 
In  fact,  exceedingly  little  is  known  concerning  the  structure 
of  much  less  complex  minerals.  Structural  formulas  have 
been  proposed,  but  these  are  conjectures  only. 

The  problem  that  confronts  the  chemist  undertaking  to 
throw  light  upon  the  constitution  of  any  of  the  products  of 
nature’s  laboratory,  is  a very  difficult  one.  No  mode  ol 
attacking  the  problem  has  ever  been  formed.  Substitutions, 
syntheses  and  decompositions  cannot  be  made  as  with 
organic  bodies.  There  is  no  means  of  estimating  the  size 
of  the  molecule.  The  question  of  determining  which  ele- 
ments are  linked  together  in  many  instances  seems  unan- 
swerable. Again,  many  elements  are  capable  of  existing 
in  two  conditions  ; this  complicates  the  problem  still  further. 
Before  attempting  to  answer  these  questions,  however,  the 
composition  of  the  body  must  be  known. 

In  a careful  review  of  the  literature  on  mineralogy,  it  will 
be  noticed  that  in  many  cases  some  constituent  of  a mineral 
has  been  determined  by  difference,  owing  probably  to  the 
fact  that  no  good  direct  method  of  estimating  it  existed  at 
that  time.  Every  chemist  feels  the  necessity  of  directly 
determining  any  constituent.  It  is  especially  desirable  that 
this  be  done  in  the  analyses  of  complex  substances.  It  may 
happen  that  many  years  have  elapsed  since  the  analysis  ot 
the  mineral  was  made.  Since  then  the  old  methods  prob- 
ably have  been  shown  to  be  inaccurate,  hence  a redetermi- 
nation is  desirable.  Owing  to  the  unreliability  of  estimating 
boric  acid,  Rammelsberg,  in  numerous  instances,  in  the 
analyses  of  tourmaline,  obtained  it  by  difference. 


p 15744 


4 


Boric  acid  constitutes  from  6 per  cent  to  12  per  cent  ot 
this  mineral.  Silica  and  alumina  are  its  common  associates 
from  which  it  is  separated  with  great  difficulty.  Since  the 
time  of  Rammelsberg,  many  methods  have  appeared,  but 
few  have  been  found  applicable  to  insoluble  borates  or 
borosilicates ; with  tourmaline,  they  have  proven  tedious  or- 
unreliable.  A chronological  review  of  the  various  methods 
for  the  determination  of  this  acid  may  be  interesting.  At 
least,  it  will  show  the  condition  in  which  the  quantitative 
determination  of  boric  acid  rests  at  the  present  time. 

| 

Historical  Resume. 

Probably  the  first  work  that  was  done  toward  the  quan- 
titative determination  of  boric  acid,  was  that  of  Arfvedson 
(K.  Vetensk.  Acad.  Handb.  1822 , 22  and  Schweigg.  Jour.  8, 
f).  By  heating  a mixture  of  borax  and  calcium  fluoride 
with  sulphuric  acid,  he  volatilized  the  boron  as  fluoride  ; the 
sodium  sulphate  resulting  from  this  treatment  was  dissolved 
out  with  water,  evaporated  to  dryness,  weighed  and  the 
boric  acid  calculated. 

Berzelius  ( Lehrbuch  3,  Aufl.  84;  Poggendorff' s Annalen 
1824 :,  2,  1 18)  attempted  the  determination  by  precipitating 
boron  as  potassium  borofluoride.  Berzelius  also  used 
Arfvedson’s  method  with  success,  but  in  place  of  the  calcium 
fluoride  and  sulphuric  acid,  he  took  hydrofluoric  and  sul- 
phuric acids. 

In  1828,  Menil  ( Jahresber . der  Chemie  undPhysik  2,  j6J) 
endeavored  to  estimate  boric  acid  by  means  of  the  silver 
salt,  3Ag20,B203,  but  met  with  little  success. 

Gay  Lussac  ( Annales  de  Chew,  et  de  Physique  40,  jg8)  in 
the  year  1830,  called  attention  to  the  titration  of  borax  by 
a sulphuric  acid  solution  with  tincture  of  litmus  as  the  indi- 
cator. The  reaction  is  : Na2B407-f-H2S04  = Na2S04-f2B203. 
The  liquid  changes  color  only  when  free  sulphuric  acid  is 
present.  This  was  the  first  volumetric  method  proposed. 


5 


Rose  {Poggendorff' s Annalen  80,  261)  was  the  first  to 
volatilize  boric  acid  as  the  ethyl  ester  and  obtain  its  amount 
by  difference.  This  was  in  1850,  but  as  early  as  1732, 
Claude  Geoffrey  knew  that  boric  acid  imparted  a character- 
istic green  color  to  the  alcohol  flame  and  in  1818,  Stro- 
meyer  {Poggendorff' s Annalen  61,  179)  mentioned  the  vol- 
atility in  an  alcoholic  solution  and  the  characteristic  green 
color  given  to  the  burning  liquid.  Rose,  in  his  paper,  gave 
a second  method,  in  which  a weighed  amount  of  sodium 
carbonate  was  added  to  the  borate,  evaporated  to  dryness 
and  ignited  until  no  further  evolution  of  carbon  dioxide. 
The  residue  of  sodium  carbonate  and  boron  trioxide  was 
weighed  and  from  this  the  boric  acid  calculated. 

Berzelius’  method  gave  poor  results,  owing  to  the  solu- 
bility of  the  precipitate  of  potassium  borofluoride  in  alcohol,, 
with  which  it  was  washed  to  free  it  from  potassium  fluoride. 
W eber  {Poggendorff  ' s Annalen , 80,  276),  1850,  tried  modi- 
fying the  method  of  Berzelius,  in  order  to  avoid  the 
formation  of  the  large  quantity  of  fluoride,  but  did  not 
succeed. 

Rammelsberg  {Poggendorff ' s Annalen , 1850,  80,  4.66) 
found  that  if  the  alcohol  used  for  washing  the  precipitate 
was  free  from  water,  potassium  fluoride  contaminated  the 
precipitate,  and  that  alcohol  containing  water  dissolved  some 
of  the  potassium  borofluoride. 

Schweitzer  {Pharm.  Centralbl.  Nr.  24,  jpo,  and  Fresenius' 
Anleituug  zur  quantit.  Analyse.  6 Aud.y  1873,  1,  424)  esti- 
mated the  base  and  determined  the  boric  acid  by  difference, 
by  evaporating  the  base  with  hydrochloric  acid  until  all  the 
acid  was  expelled  and  estimating  the  chlorine  as  silver 
chloride. 

In  1856,  Kraut  {Hennebergs  Jour,  fur  Landwirtsch.  4, 
1 12  ; abs.  by  Zeit.  fur  analyt.  Chemie  1863 , 73)  showed  that 
a borax  solution  boiled  with  ammonium  chloride,  reacted 
according  to  the  following  equation  : Na2B407T  2NH,CI"= 


6 


2NaCl+2B203-f  2NH3,  and  the  ammonia  could  be  caught  in 
a standard  acid  solution,  and  thus  the  boric  acid  determined. 

This  same  year,  the  method  of  Stromeyer  (Liebig* s Anna- 
len , ioo,  82)  appeared.  He  added  to  the  solution  of  the 
borate  two  equivalents  of  potassium  hydrate  to  one  equiva- 
lent of  boron  trioxide  contained  in  the  borate,  then  an 
excess  of  hydrofluoric  acid  and  evaporated  to  dryness.  The 
residue  he  dissolved  in  a 20  per  cent  solution  of  potassium 
acetate,  and  filtered  through  a weighed  filter,  using  a gutta 
percha  funnel.  The  precipitate  was  washed  first  with  a 
solution  of  potassium  acetate  to  remove  potassium  fluoride, 
then  with  alcohol,  dried  at  ioo°  C.  and  weighed.  Upon 
applying  this  method  to  a silicate,  Stromeyer  obtained  97.5 
per  cent  of  all  the  boron  trioxide. 

Where  the  boric  acid  content  was  approximately  known, 
Schafifgotsch  [Poggendorff'  s Anua/en,i8y^t  107,  42  f)  added 
to  the  solution  a weighed  amount  of  sodium  carbonate,  in 
which  not  less  than  one  and  not  more  than  two  equivalents 
of  sodium  oxide,  Na20,to  two  equivalents  of  boron  trioxide 
were  contained.  After  evaporation  to  dryness  and  ignition, 
the  residue  was  sodium  oxide  and  boron  trioxide,  the  weight 
of  which  less  the  weight  of  the  sodium  oxide  taken,  gave 
the  boron  trioxide.  This  method  is  essentially  the  same  as 
that  of  Rose. 

Marignac  (Zeit.  fur  analyt.  Chemie  1862 , 1,  405)  in  a 
solution  containing  alkali  salts  only,  estimated  the  boric 
acid  thus  : After  the  addition  of  magnesium  chloride,  am- 
monium chloride  and  ammonia,  he  evaporated  the  solution 
to  dryness  in  a platinum  dish.  The  residue  after  ignition  was 
taken  up  with  water  and  the  insoluble  portion  removed  : the 
filtrate  was  made  ammoniacal,  evaporated  to  dryness,  ignited, 
the  residue  taken  up  with  water  and  the  insoluble  portion 
filtered  off  as  before.  This  was  repeated  three  times.  The 
insoluble  portions  were  ignited  and  weighed  as  magnesium 
pyroborate ; the  magnesia  was  determined  by  dissolving 


7 


the  pyroborate  in^nitric  acid  and  precipitating  as  magnesium 
ammonium-phosphate,  and  from  this  the  boric  acid  was 
obtained  by  difference.  Insoluble  borates  were  fused  with 
sodium  carbonate,  the  melt  extracted  with  water  and  the 
solution  acidified  with  hydrochloric  acid;  ammonia  was 
then  added  and  the  whole  concentrated  to  a small  volume. 
Any  precipitate  that  formed  was  filtered  off : any  lime 
present  was  removed  as  oxalate.  The  solution  was  then 
supposed  to  contain  the  borate  together  with  alkali  salts 
and  was  ready  for  the  treatment  with  magnesium  chloride 
solution.  In  regard  to  this  method,  Marignac  himself says  : 
“ If  good  results  are  obtained,  it  is  due  to  a balancing  of 
errors.” 

'R.osz^Handb.  der  analyt.  Chemic  6 Aufl.  2,  721),  1871, 
substituted  sodium  metaborate  for  the  sodium  carbonate 
used  in  his  earlier  method. 

By  fusing  boric  acid  with  calcium  chloride  in  the  pres- 
ence of  sodium  and  potassium  chlorides,  Ditte  ( Comptes 
rendus , 1873,  80,  490,  a?id  561)  obtained  the  salt  Ca0,B203 
which  crystallized  from  the  fusion  in  needles  and  was  insolu- 
ble in  cold  water.  He  utilized  this  salt  for  the  estimation 
of  the  acid. 

In  1877,  Berg  (Zeit.  fur  analyt.  Chemie  22,  25)  precipi- 
tated from  an  alcoholic  solution  Ba0,B203  4H20.  The 
precipitation  was  fairly  complete,  enabling  him  to  determine 
boron  trioxide  in  borax  and  obtain  results  within  .1  per  cent 
to  .3  per  cent  of  the  theoretical  amounts. 

Smith  {Am.  Chew.  Jour.  1882-83 . 279)  precipitated 

manganese  borate,  MnO,  2B203,  from  a borax  solution  in 
the  presence  of  alcohol  and  determined  the  excess  of  man- 
ganous sulphate  added,  by  evaporating  the  filtrate  from  the 
manganese  borate  to  dryness,  taking  up  with  water  and 
titrating  the  manganese  according  to  Volhard. 

In  applying  this  method  to  a silicate,  the  latter  was  fused 
with  sodium  carbonate,  the  melt  extracted  with  water 


8 


and  the  solution  digested  with  ammonium  sulphate  to 
throw  out  silica  and  alumina.  After  removing  these,  a 
known  amount  of  manganous  sulphate  solution  with  an 
equal  volume  of  alcohol  was  added ; the  precipitate  was 
removed  and  the  manganese  in  the  filtrate  determined  as 
above.  In  a tourmaline,  the  percentage  of  boric  acid  found 
by  Marignac’s  method  was  io  per  cent,  while  that  found  by 
Smith’s  method  was  9.7  per  cent.  Bodewig  (Zeit  fur  anaylt. 
Chemie  1884.,  23,  /^p)  tried  the  method  of  Smith  upon  a 
silicate,  but  obtained  no  result. 

With  some  success,  Bodewig  used  Stromeyer’s  method 
in  the  determination  of  the  free  acid,  but  upon  applying  it 
to  a silicate,  he  experienced  considerable  difficulty  in 
obtaining  a solution  of  the  borate  free  from  silica.  To 
accomplish  this,  the  procedure  of  Berzelius  (use  of  an 
ammoniacal  zinc  oxide  solution)  was  resorted  to  with  a 
fair  degree  of  success. 

The  methods  of  Gooch  and  Rosenbladt  appeared  sim- 
ultaneously in  1 887.  Gooch  (Am.  Chem.  Jour.  9,  2j ) 
evaporated  the  solution  of  free  boric  acid  to  dryness  with  a 
weighed  amount  of  lime  and  ignited  to  constant  weight. 
The  increase  in  weight  represented  boron  trioxide.  Rosen- 
bladt (Zeit.  fur  analyt.  Chemie  26,  21)  used  magnesia  in 
place  of  lime. 

Both  Gooch  and  Rosenbladt  showed  that  boric  acid  could 
be  completely  expelled  from  the  concentrated  acid  solution 
of  a borate  as  the  methyl  ester.  To  accomplish  this,  Gooch 
used  an  apparatus  consisting  of  a large  pipette  bent  at  one 
end  of  the  bulb  at  a right  angle  and  at  the  other  like  a 
goose  neck ; the  end  of  the  pipette  extended  into  a con- 
denser. Insoluble  borates  were  fused  with  sodium  carbon- 
ate; the  melt  was  extracted  with  water  and  the  solution 
evaporated  to  dryness  in  the  bulb  of  the  pipette,  which  was 
immersed  in  a paraffin  bath.  The  residue  was  made  acid 
with  nitric  or  acetic  acid  and  the  distillation  with  methyl 


9 


alcohol  begun  ; the  methyl  alcohol  was  added  in  portions 
of  io  c.  c.  The  distillate  was  poured  into  a platinum  dish, 
containing  a weighed  amount  of  lime,  evaporated  to  dry- 
ness and  ignited  to  constant  weight ; the  increase  in  weight 
represented  boron  trioxide. 

The  apparatus  used  by  Rosenbladt  was  more  simple  than 
that  used  by  Gooch.  It  consisted  essentially  of  an  Erlen- 
meyer  flask  connected  with  a condenser.  Rosenbladt’s 
method  differed  from  Gooch’s  only  in  that  the  ester  was 
caught  in  an  ammonium  carbonate  solution  then  poured 
into  a dish  containing  a weighed  amount  of  magnesia  and 
evaporated  to  dryness. 

Morse  and  Burton  ( Am . Chem.  Jour.  1888,  10,  154)  to  a 
concentrated  borax  solution  of  small  volume,  added  sul- 
phuric acid  to  acid  reaction  using  tropaeoline  00  as  the 
indicator.  After  the  addition  of  anhydrous  copper  sulphate, 
the  resulting  mass  was  extracted  with  absolute  alcohol ; 
this  alcoholic  solution  was  run  into  an  excess  of  standard 
barium  hydrate.  The  excess  of  baryta  was  changed  to 
carbonate,  the  whole  evaporated  to  dryness  and  weighed  as 
barium  carbonate  and  barium  metaborate,  from  which  the 
boric  acid  was  calculated.  Insoluble  borates  were  decom- 
posed by  fusion  with  sodium  hydrate  in  a nickel  crucible. 
The  extract  of  the  fusion  was  evaporated  to  a small  bulk 
and  treated  as  the  borax  solution.  By  this  procedure, 
Morse  and  Burton  obtained  from  a tourmaline  the  follow- 
ing percentages  of  boron  trioxide : 10.03  Per  cent,  10.08 
percent  and  10. n per  cent.  Dr.  Riggs  obtained  from  the 
same  tourmaline  by  a different  method  10.15  per  cent,  10.00 
per  cent  and  10.31  per  cent. 

By  means  of  a solution  of  baryta,  Will  (Archiv.  der 
Pharmacie  225,  iioi>  abs.  by  Zeit.fur  analyt . Chemie  i88g , 
28,  100)  titrated  boric  acid. 

Kriiss  and  Moraht  {Liebig's  Annalen  18 go,  259,  184)  in 
the  analysis  of  beryllium  borate,  gave  the  method  of 
Stromeyer  preference. 


IO 


To  the  salt  of  the  alkali  metal,  Parmentier  ( Comptes 
rendus  1891,  113,  41)  added  an  excess  of  hydrochloric  acid 
or  sulphuric  acid.  After  dividing  the  solution  into  two 
equal  parts,  he  added  to  one  methyl  orange  and  titrated  the 
excess  of  hydrochloric  or  sulphuric  acid : to  the  other, 
litmus  was  added  and  the  total  acidity  determined.  The 
difference  gave  the  boric  acid.  Reischle  {Zeit.  fiir  anorg . 
Chemie  189J , 4,  ///)  stated,  that  the  color  reaction  of  the 
litmus  was  so  indistinct  that  he  could  obtain  no  results. 

In  1893,  Thompson  {Jour.  Soc.  them.  Ind . 12,  432) 
noticed  that  a boric  acid  solution  containing  30  per  cent  of 
glycerol  could  be  titrated  with  sodium  hydrate  with  phe- 
nolphthalein  as  the  indicator.  Starch,  glucose  and  cane 
sugar  could  be  substituted  for  glycerol.  In  borax  the  acid 
was  set  free  by  hydrochloric  acid  using  methyl  orange  as 
the  indicator  and  the  boric  acid  titrated  by  a solution  of 
sodium  hydrate  with  glycerol  and  phenolphthalein. 
Thompson  applied  this  method  to  boracite. 

As  the  commercial  method  of  estimating  boron  trioxide 
in  boronatro  calcites,  Le  Roy  {Jour.  Soc.  Chem . Ind.  1893 , 
867)  gave  the  following:  Decompose  the  mineral  with 
dilute  sulphuric  acid  and  hydrochloric  acid  in  a flask  con- 
nected with  a reflux  condenser:  remove  the  insoluble  residue 
and  precipitate  the  iron  and  aluminium  as  hydrates  by  caus- 
tic soda.  After  the  removal  of  these,  the  solution  is  made 
acid  with  hydrochloric  acid  and  boiled  to  expel  carbon 
dioxide ; upon  cooling,  it  is  made  up  to  a known  volume. 
Twenty  cubic  centimeters  of  this  solution  are  titrated  with 
standard  alkali  and  Porrier  orange  ill,  until  the  shade 
produced  corresponds  to  the  yellowish  red  caused  by  the 
same  amount  of  orange  1 1 1 in  20  c.c.  of  water.  Another 
volume  of  20  c.c.  is  now  titrated  with  alkali  using  orange 
1 1 as  the  indicator,  until  the  color  is  a dark  red.  The  dif- 
ference between  the  two  titrations  indicates  the  boric  acid 
present. 


Schwarz  ( Pharm . Zeitung  1894.,  32,  362)  suggested  Congo 
Red  as  an  indicator  to  be  used  with  hydrochloric  acid. 
Hefelmann  (Pharm.  Centralhalle  (N.  P)  1894,  9,  116)  gave 
litmus  the  preference. 

Hefelmann  recommends  the  expulsion  of  the  boric  acid 
by  heating  with  ammonium  fluoride  and  the  estimation  of 
it  by  difference. 

Barthe  (Jour.  Pharm.  Chem.  1894 , 29,  163)  used  the 
method  of  Thompson  with  success  as  did  also  Honig  and 
Spitz  (Zeit.  fiir  angewandte  Chemie  1896 , jjo).  Insoluble 
silicates  were  fused  by  the  latter  with  sodium  and  potassium 
carbonates.  The  melt  was  dissolved  in  water  and  as  much 
ammonium  chloride  added  as  equaled  the  carbonates  used 
in  the  fusion.  The  solution  was  then  boiled  and  the  pre- 
cipitated silica  removed.  The  last  traces  of  silica  were 
removed  by  Berzelius’  method.  After  concentration 
to  a small  volume,  the  liquid  was  made  acid  with  hydro- 
chloric acid,  boiled  a few  minutes  to  expel  carbon 
dioxide  and  titrated.  By  this  procedure,  the  percentage 
of  boron  trioxide  found  in  a “ Gasgliihlicht-cylinder  ” 
was  5.12  per  cent,  while  that  found  by  difference  was  5.34 
per  cent. 

Honig  and  Spitz  also  applied  the  reaction  made  use  of 
by  Kraut — Na2B407  -f  2NH4C1  = 2NH3  -f-  2NaCl  -f- 
2B203 — to  “ Boraxkalk.”  The  results  obtained  differed 
.10  per  cent  to  .30  per  cent  from  those  got  by  their  first 
method. 

In  1897,  Kraut  (Zeit.  fur  analyt.  Chemie  36,  165)  em- 
ployed Gooch’s  method  successfully  for  the  analysis  of 
colemanite  and  pandermite.  The  apparatus  used  in  the 
distillation  of  the  ester  was,  however,  more  simple  than  that 
of  Gooch. 

Schneider  and  Gaab  (Pharm.  Centralhalle  1897,  37,  672) 
distilled  the  boric  acid  with  alcohol  and  evaporated  the  dis- 
tillate with  a weighed  amount  of  sodium  carbonate. 


12 


By  shaking  with  ether,  Beliocq  (Rev.  Int.  falsific.  9,  119 , 
abs.  by  Zeit.  fur  anorg.  Chemie  1897,  380 ) removed  boric 
acid  from  other  salts,  and  upon  the  evaporation  of  the 
ethereal  extract  obtained  the  trioxide. 

Thaddeeff  (Zeit.  fur  analyt.  Chemie  1897,  36, 368)  applied 
the  Berzelius-Stromeyer  method,  somewhat  modified,  to 
borax.  His  modification  consisted  in  adding  to  the  potas- 
sium acetate  solution  containing  the  potassium  borofluo- 
ride,  100  c.c.  of  alcohol  .805  sp.  gr.  and  allowing  it  to 
stand  twelve  to  fourteen  hours  before  filtering.  The  pre- 
cipitate was  washed  with  alcohol  of  the  same  specific 
gravity.  By  this  means,  results  varying  from  .08  per  cent 
to  .40  per  cent  of  the  theoretical  were  obtained.  Thad- 
deeff also  volatilized  boric  acid  as  the  methyl  ester  which 
was  caught  in  a solution  cf  potassium  hydrate.  From  this 
potassium  borofluoride  was  precipitated.  To  facilitate  the 
volatilization  of  the  ester,  Thaddeeff  used  a current  of  air. 
By  this  procedure,  he  obtained  results  varying  from  .01 
per  cent  to  .40  per  cent  of  the  theoretical. 


INVESTIGATION. 


From  this  review,  it  is  apparent  that,  while  boric  acid  in 
borax,  soluble  borates  and  minerals  not  requiring  fusion 
with  alkalies  for  their  decomposition,  is  estimated  with  a 
fair  degree  of  success,  this  acid,  where  fusion  is  required,  is 
not  determined  with  the  desired  accuracy. 

Minerals  containing  silica  and  alumina  usually  require 
fusion  with  sodium  carbonate  or  caustic  soda  for  their 
decomposition.  The  extract  from  this  fusion  is  supposed 
to  contain  all  the  boric  acid  together  with  silicate  and 
aluminate  of  soda.  Digestion  with  ammonium  chloride  or 
sulphate  is  generally  resorted  to  for  the  removal  of  the  latter 
two.  The  solution  is  then  ready  for  treatment  according  to 
any  method  applicable  to  borax. 


13 


The  methods  of  Gooch,  Stromeyer  and  Marignac  have 
been  universally  used.  If  Marignac’s  method  is  adopted, 
results  are  obtained  about  which  there  is  more  or  less 
uncertainty.  If  Stromeyer’s  method  is  used,  the  potassium 
borofluoride  weighs  more  than  it  should,  owing  to  fluosili- 
cate  ( Fresenius ’ Quant.  Chem . Anal.  424).  To  avoid  this 
silica,  Wohler  [Handb.der  Mineral  Analyse , under  Datholite) 
recommends  evaporating  the  hydrochloric  acid  solution  of 
the  fusion  to  dryness,  in  a flask  connected  with  a condenser, 
adding  the  distillate  to  the  residue  and  filtering  off  the 
silica.  By  this  means,  silica  is  entirely  removed,  but 
alumina  and  other  bases  are  yet  to  be  separated,  and  in 
the  removal  of  the  alumina  as  hydrate,  there  is  a 
tendency  on  the  part  of  the  precipitate  to  retain  boric 
acid  ( Wohler , Ann.  der  Chem.  und  Pharm.  141,  268).  In 
the  use  of  Gooch’s  method  the  trouble  is  met  in  weighing 
the  lime. 

It  is  evident  from  the  foregoing,  that  the  quantitative 
determination  of  this  acid,  where  it  exists  in  such  combina- 
tion as  it  does  in  tourmaline,  is  not  attended  with  the  most 
desirable  results.  With  the  hope  of  obtaining  a more 
accurate  and  more  rapid  method  and  of  casting  some  light, 
perhaps,  upon  the  constitution  of  this  mineral,  this  investi- 
gation was  undertaken. 

The  isolation  of  the  acid  is  evidently  necessary  for  its 
successful  determination.  Its  separation  from  these  two 
associates,  silica  and  alumina,  is  difficult,  and  alkalies 
apparently  increase  this  difficulty;  hence  it  was  thought,  if 
the  tourmaline  could  be  decomposed  by  heating  with 
metallic  magnesium  or  fusion  with  carbonates  other  than 
those  of  the  alkalies,  the  isolation  of  the  boric  acid  would 
be  more  readily  accomplished  ; or  if  the  tourmaline  was 
fused  with  alkali  carbonates,  possibly  it  could  be  completely 
removed  from  these  objectionable  associates  in  an  acid 
solution. 


Since  the  volumetric  method  of  Thompson  seemed  to 
offer  the  most  rapid  and  accurate  means,  I decided  to 
investigate  it,  with  the  view  of  utilizing  it  for  the  determi- 
nation of  the  isolated  boric  acid. 


Determination  of  Boric  Acid  in  Borax  by  the 
Method  of  Thompson. 

One-tenth  normal  hydrochloric  acid  solution  was  pre- 
pared and  standardized  by  precipitating  the  chlorine  with 
silver  nitrate. 

No.  i,  10  c.c.  HC1  sol.  gave  .1430  gram  AgCl  = .035358 
gram  Cl. 

No.  2,  10  c.c.  HC1  sol.  gave  .1440  gram  AgCl  = .035605 
gram  Cl. 

Average  = .035481  gram  Cl. 

Theory  = .03545  “ “ 

Difference  = .000031  “ “ 

From  this  hydrochloric  acid  solution  a tenth  normal 
caustic  soda  solution  was  prepared.  A borax  solution,  10 
c.c.  of  which  contained  1 gram  of  Na2B407,  ioH20,  or 
.03659  gram  of  B203,  was  prepared  from  recrystallized 
borax.  As  nearly  all  glycerol  is  likely  to  be  acid  owing  to 
fatty  acids,  it  was  found  best  to  add  a very  small  amount  of 
water  to  the  glycerol,  then  phenolphthalein,  shake  well, 
and  introduce  sodium  hydrate  until  a faint  pink  tinge 
appeared.  This  neutralized  glycerol  was  kept  in  a well 
stoppered  bottle. 

For  the  estimation  of  boric  acid  in  the  latter,  a number 
of  c.c.  of  the  borax  solution  were  introduced  into  an 
Erlenmeyer  flask,  a few  drops  of  methyl  orange  added  and 
tenth  normal  hydrochloric  acid  run  in  from  a burette  until 


15 


all  the  boric  acid  was  free : 50  c.c.  of  the  glycerol  were 
added,  together  with  a few  drops  of  phenolphthalein,  and 
the  titration  with  tenth  normal  caustic  soda  begun.  Accord- 
ing to  the  reaction : 2B203  -f-  4NaOH  =4NaB02  + 2H20, 
1 c.c.  of  tenth  normal  alkali  is  equivalent  to  .0035  gram 
of  B203. 

The  following  table  shows  the  value  of  this  method  : 

Taken.  Found. 


Borax  sol. 

B0O3. 

N 

— NaOH 

B2O3. 

No. 

C.C. 

Grams, 

C.C. 

Grams. 

Per  Cent. 

I 

...  10  .03659 

IO.4 

•0364 

36.40 

2 

...  10  .03659 

10.5 

.03675 

36.75 

3 

...  10  .03659 

IO.4 

.3640 

36.40 

4 

...  20  .07318 

21.0 

•0735 

36.75 

5 

...  20  .07318 

20.9 

•07315 

36.57 

6 

...  25 

.O9I47 

26.1 

•09135 

36.54 

7 

...  25 

.09147 

26.1 

•09135 

36.54 

8 

...  15 

.O5488 

15*7 

•05495 

36.63 

9 

...  15 

.O5488 

157 

•05495 

3663 

10 

...  15 

.05488 

15.6 

.0546 

36.40 

The  atomic  weights  used  were  : 

Oxygen  — 16.00  Boron  = 10.95 

Silver  = 107.97  Chlorine  = 35.45 

Sodium  = 23.05 

The  theoretical  percentages  of  the  constituents  of  crys- 
tallized borax  are  : 

Na20  = 16.26  per  cent. 

BA  = 36.59  “ 

H30  = 47-15  “ 

Having  proved  the  volumetric  method  of  Thompson  to 
give  reliable  results  with  borax,  the  problem  of  isolating  the 
boric  acid  in  tourmaline  was  taken  up. 


i6 

Decomposition  of  Tourmaline  by  Heating  with 
Metallic  Magnesium. 

Two-tenths  of  a gram  of  brown  tourmaline  (No.  2)  was 
heated  to  expel  the  water,  mixed  with  half  a gram  of  mag- 
nesium powder,  the  whole  placed  in  a porcelain  crucible 
and  covered  with  a thick  layer  of  thoroughly  dried  salt. 
It  was  then  heated  for  thirty  minutes  and  allowed  to  cool. 
The  contents,  which  had  the  appearance  of  amorphous  sili- 
con, together  with  any  parts  of  the  crucible  to  which  the  con- 
tents adhered,  were  powdered,  placed  in  a porcelain  boat  and 
chlorine  passed  over  the  same.  The  chlorine  and  any  volatile 
portion  were  caught  in  two  U tubes  containing  water ; later, 
heat  was  applied  and  gradually  raised  to  a dull  red,  where 
it  was  held  until  the  contents  of  the  boat  became  quiescent. 
The  heat  was  then  gradually  withdrawn.  After  four  days, 
most  of  the  chlorine  had  gone  from  the  U tubes,  leaving 
the  contents  exceedingly  acid.  Sodium  carbonate  suffi- 
cient to  neutralize  the  acid  was  added,  and  the  solution 
evaporated  almost  to  dryness.  After  making  acid  and 
expelling  the  carbon  dioxide  by  drawing  air  through  the 
solution  for  fifteen  minutes,  the  excess  of  acid  was  neutral- 
ized by  sodium  hydrate  with  methyl  orange  as  the  indicator, 
and  the  boric  acid  titrated  with  the  following  results : 


Weight  of  Mineral.  — Na  OH.  B203.  PerCent. 

10 

No.  Grams.  C.  C.  Grams. 

1  2000  5.0  .0175  8.75 

2  2000  2.5  .00875  4-357 

3  2000  1.2  .0042  2.10 

4  2000  20  .007  3.50 

5 ....  . .2000  1.5  .00525  2.625 


Number  four  was  allowed  to  stsnd  two  days  before  treat- 
ing the  contents  of  the  U tubes.  Very  little  acid  was  present. 
Numbers  two,  three  and  five  were  allowed  to  stand  but  a 


i7 


few  hours  before  treating.  Little  acid  was  present  and  the 
chlorine  was  removed  in  each  instance  before  the  addition 
of  the  sodium  carbonate,  by  drawing  air  through  the  tubes. 

It  might  be  added,  that  the  time  of  heating  the  mineral 
with  the  magnesium  powder  was  varied  from  fifteen  minutes 
to  an  hour,  and  in  every  case  the  contents  of  the  crucible 
had  the  appearance  of  amorphous  silicon. 

This  procedure  is  evidently  not  a success;  just  why,  I do 
not  know,  but  am  inclined  to  believe  that  the  boron  chloride 
was  not  completely  broken  up  when  it  came  in  contact  with 
the  water  saturated  with  chlorine,  but  was  carried  on  out  with 
the  escaping  gas.  It  may  have  been  that  the  mineral  was 
not  completely  decomposed  by  the  magnesium,  but  from 
all  appearances  the  magnesium  had  entirely  reduced  it. 

At  any  rate,  this  procedure  was  abandoned,  and  the 
fusion  of  the  mineral  with  the  alkali-earth  carbonates  under- 
taken. 

Decomposition  of  Tourmaline  by  Fusion  with  Calcium 
Carbonate. 

Some  of  the  very  finely  powdered  mineral  was  fused  with 
a mixture  of  eight  times  its  weight  of  precipitated  calcium 
carbonate  and  once  its  weight  of  ammonium  chloride,  at  a 
low  red  heat  for  one  hour,  as  in  the  J.  Lawrence  Smith 
fusion  for  the  alkalies ; when  cool  the  fusion  was  powdered, 
placed  in  a platinum  dish,  covered  with  water  and  an 
amount  of  sodium  carbonate  introduced  slightly  in  excess 
of  that  required.  After  digesting  for  half  an  hour  the  solu- 
tion was  allowed  to  cool  and  the  insoluble  portion  was 
removed.  To  the  filtrate  sulphuric  acid  to  almost  neutral 
reaction  was  added.  The  precipitate  which  formed  was  fil- 
tered off  and  the  solution  made  slightly  acid.  For  fifteen 
minutes  air  was  drawn  through  the  solution  to  remove 
the  carbon  dioxide,  after  which  the  excess  of  acid  was 


i8 


neutralized  with  caustic  soda,  with  methyl  orange  as  the 
indicator,  and  the  boric  acid  titrated. 

In  this  instance  half-normal  sodium  hydrate  was  used  in 
the  titration  of  the  boric  acid.  One  cubic  centimeter  of  a 
half-normal  alkali  solution  is  equivalent  to  .0175  gram  of 
boron  trioxide.  The  results  are  shown  in  this  table : 

Weight  of  Mineral  (No.  2)-  — NaOH.  B206. 

2 


No.  Grams.  C.  C.  Grams.  Per  Cent. 

1  3OOO  2.4  .0420  I4.OO 

2  3OCO  2.8  .O49O  16.33 

3  3000  3.7  .06475  21.58 


The  decomposition  of  the  mineral  was  complete,  because 
all  the  portion  insoluble  in  water,  except  silica,  dissolved  in 
hydrochloric  acid. 

Upon  allowing  the  titrated  solutions  to  stand,  in  every  case 
a precipitate  of  alumina  separated.  Thinking  that  during 
the  boiling  of  the  fusion  with  soda  some  alumina  was  dis- 
solved, I used  barium  carbonate  in  the  place  of  the  soda  and 
decomposed  the  fusion  by  boiling  with  sodium  sulphate, 
with  the  hope  of  avoiding  the  solution  of  alumina. 

That  this  was  not  a success  is  shown  by  the  following : 

Weight  of  Mineral  (No.  2).  — NaOH.  B203 

2 


No.  Grams.  C.C.  Grams.  Per  Cent. 

1  3000  1.5  .02625  8.7  5 

2 3000  3.3  .05775  I9.25 

3  3000  4.3  -07525  25.08 

4  3000  2.6  -0455  *5.16 

5  3000  2.1  .03675  12.25 

6  3000  1.85  .3237  10.79 


In  every  instance,  after  titration,  a copious  precipitate  of 
alumina  came  down  upon  boiling  with  hydrochloric  acid 
and  adding  an  excess  of  ammonia. 

It  is  very  likely  that  in  the  digestion  of  the  fusion 
with  sodium  sulphate,  barium  carbonate  becomes  barium 


19 


sulphate  and  sodium  carbonate  is  formed,  this  then  dis- 
solves the  alumina. 

I thought  that  possibly  this  alumina  might  be  eliminated 
completely  by  adding  a small  quantity  of  ammonium  sul- 
phate to  the  sodium  sulphate  solution  free  from  the  insolu- 
ble portion,  and  digesting  with  a reflux  condenser;  the 
ammonia  could  easily  be  expelled  by  boiling  with  an  excess 
of  alkali.  This  was  done  and  the  following  results 
obtained  : 

N 

Weight  of  Mineral  (No.  2).  — NaOH.  b203. 


No.  Grams.  C.  C.  Grams.  Per  Cent. 

1  5000  2.6  .0455  9.10 

2 5000  2.25  .O3937  7.87 

3  5000  2.00  .0350  7.00 


Upon  testing  after  the  titration,  alumina  was  found. 

The  insoluble  portions  of  some  of  these  fusions  were 
fused  with  sodium  carbonate  and  the  boric  acid  therein, 
determined  by  distillation  with  methyl  alcohol — a method 
which  will  be  given  later — and  the  following  amounts 
found : 

N 

Weight  of  Mineral  (No.  2).  2 B203. 


No.  Grams.  C.  C.  Grams.  Per  Cent. 

2 3000  1. 1 .OI925  6.41 

3  3000  0.6  .0105  3.50 

1  5000  1.0  .0175  3.50 

2  5000  1. 1 .01925  3.85 

3  5000  1.4  .0245  4.90 


From  this  it  appears  that  the  decomposition  of  tourma- 
line by  fusing  the  mineral  with  calcium  or  barium  carbonate 
does  not  succeed ; nor  is  it  a success  with  datolite,  as  the 
following  show : 

N 

Weight  of  Mineral.  2 B203. 


No.  Grams.  C.  C Grams.  PerCent. 

1  5000  4.6  .0805  l6.IO 

2  30C0  2.8  .O49O  16.33 


20 


The  decompositions  were  complete,  but  some  boric  acid 
had  remained  with  the  insoluble  portions. 

Tourmaline  to  be  completely  decomposed  must  be  fused 
with  alkalies.  Then  if  boric  acid  is  to  be  cleanly  removed 
from  the  alumina,  it  must  be  done  in  an  acid  solution.  The 
methods  of  Gooch  and  Rosenbladt  are  the  only  means  of 
accomplishing  this  and  directly  esti- 
mating the  boric  acid ; but  the  process 
as  practiced  by  Gooch  or  Rosenbladt  is 
rather  slow.  Thaddeeff  lessened  the 
time  necessary  for  the  complete  removal 
of  the  boric  acid  as  the  methyl  ester,  by 
using  a current  of  air. 

By  utilizing  the  discovery  of  Gooch 
and  Rosenbladt  and  the  volumetric 
method  of  Thompson,  I thought  a rapid 
and  accurate  method  could  be  devised. 

The  Volatilization  of  the  Boric 
Acid  as  the  Methyl  Ester  and 
Subsequent  Titration. 

To  diminish  the  time  required  for  the 
complete  volatilization,  this  apparatus, 
the  plan  of  which  is  here  shown,  was 
constructed. 

A weighed  amount  of  fused  borax 
was  placed  in  the  bulb,  moistened  with 
sulphuric  acid,  io  c.  c.  of  commercial  wood  alcohol  added 
and  the  distillation  begun.  The  distillate  was  caught  in 
the  flask  B,  which  contained  25  c.  c.  of  tenth  normal 
caustic  soda,  into  which  the  condenser  tube  extended 
about  one  inch.  When  nearly  all  the  alcohol  had  distilled 
over,  air  was  drawn  through  the  whole  apparatus  for  a 
few  minutes,  by  attaching  a suction  pump  to  A and 
opening  the  stopcock  at  D sufficiently  far  to  let  the  air 


21 


gently  bubble  through  the  solution  in  B.  This  operation 
was  repeated  until  50  c.  c.  of  wood  alcohol  had  been  added 
and  distilled  off  into  the  sodium  hydrate.  The  flask  was 
disconnected,  25  c.  c.  of  tenth  normal  hydrochloric  acid 
were  introduced,  then  100  c.  c.  of  glycerol  with  a few  drops 
of  phenolphthalein  and  the  titration  of  the  boric  acid  with 
tenth  normal  alkali  begun.  By  this  procedure  the  following 
results  were  obtained  : 


No. 

Taken 

Weight  of  Borax. 
Grams. 

b2o3. 

Grams . 

Found 

N 

— NaOH. 

10 

C.  C. 

b2o3. 

Grams. 

Per  Cent. 

I . 

. . . .1000 

.O6924 

23.OO 

.0805 

80.50 

2 . 

. . . .1000 

.O6924 

22.80 

.0794 

79.80 

The  theoretical  percentages  of  the  constituents  of  fused 
borax  are : 


Na20  ....  30.76.  B203  ....  69.24. 

The  amount  of  alcohol  in  each  case  being  the  same  and 
the.  results  obtained  agreeing  so  closely,  I concluded  that 
the  alcohol  was  the  cause  of  the  high  percentages. 

Upon  evaporating  the  distillate  obtained  as  above  and 
igniting,  a black  charred  mass  was  left,  which,  however, 
was  easily  burned.  This  showed  either  that  some  organic 
compound  had  been  formed  in  the  distillation  of  the  alcohol 
from  the  sulphuric  acid  or  existed  as  an  impurity  in  the 
alcohol  and  was  carried  over  during  the  distillation.  If  the 
substance  were  acetic  acid  or  formic  acid,  the  sodium  salt 
would  be  formed,  which  when  treated  with  hydrochloric 
acid  would  regenerate  the  acid  and  thus  increase  the  amount 
of  sodium  hydrate  required. 

To  ascertain  whether  a formate  was  produced,  some  pure 
methyl  alcohol  was  distilled  with  sulphuric  acid.  The  dis- 
tillate which  was  caught  in  caustic  soda,  was  concentrated, 
the  alkali  neutralized  with  nitric  acid  and  silver  nitrate 
added.  The  odor  of  formic  acid  was  distinctly  perceptible 


22 


upon  neutralizing  the  sodium  hydrate,  and  upon  adding  the 
silver  nitrate  and  boiling,  silver  separated.  When  the  ester 
comes  in  contact  with  the  alkali,  the  probable  reaction  is  : 
B(0CH3)3+Na0H  + H20=B00Na-l-CH30H.  The  heat- 
ing of  methyl  alcohol  with  sulphuric  acid  in  the  air  seems 
to  react  thus  : CH3OH+ 02=H20  + HC00H. 

To  destroy  this  organic  acid,  the  distillate  was  evaporated 
to  a small  volume,  carbon  dioxide  rapidly  run  through  to 
insure  the  formation  of  borax,  the  evaporation  then  con- 
tinued to  dryness  and  the  residue  ignited  until  all  the  car- 
bon was  consumed.  When  cool,  hydrochloric  acid  was 
added  in  slight  excess  and  the  carbon  dioxide  removed  by 
drawing  air  through  the  solution  for  a quarter  of  an  hour. 
The  excess  of  hydrochloric  acid  was  neutralized  and  the 
boric  acid  titrated  with  half  normal  sodium  hydrate. 


Taken.  Found. 


Weight  of  Borax. 

b2o3. 

E.Na0H. 

10 

b2o3 

No. 

Grams. 

Grams. 

c.c. 

Grams. 

Per  Cent. 

I . 

. . .2000 

.13848 

9.0 

•1575 

78.7s 

2 . 

. . .2000 

.13848 

8.2 

•1435 

71-75 

3 * 

. . .1000 

.06924 

4.0 

.0700 

70.00 

These  results  are  too  high  and  variable,  so  pure  methyl 
alcohol  was  substituted  for  the  commercial  article  and  about 
60  c.c.  were  used  each  time.  The  boric  acid  was  titrated 
in  this  instance  with  tenth  normal  caustic  soda.  It  will  be 
noticed  that  sometimes  tenth  normal  alkali  was  used  in  the 
titration,  and  at  other  times  half  normal.  Either  gave  good 
results  in  the  titration  of  boric  acid  in  borax,  but  with  half- 
normal sodium  hydrate,  the  end  reaction  was  more  pro- 
nounced. 


Taken.  Found. 


Weight  of  Borax. 

b2o3. 

E NaOH. 

IO 

b2o3. 

No. 

Grams. 

Grams . 

c.c. 

Grams. 

Per  Cent. 

I . 

. . .5000 

.3462 

97-5 

•34125 

68.25 

2 . 

. . .2000 

.13848 

39-5 

00 

eo 

69.13 

3 • 

. . .3OOO 

.20772 

58.8 

.2058 

68.60 

23 


According  to  these  reactions : 4B(OH)3-}-4NaOH= 
4B0,0Na-|-8H20  and  4BO,OH+4NaOH=4BO,ONa+ 
3H2O,  the  treatment  with  carbon  dioxide  was  unnecessary 
and  was  dispensed  with  in  the  following  determinations : 


Taken.  Found. 


Weight  of  Borax. 

B2O3. 

NaOH. 

10 

B2O3. 

No. 

Grams. 

Grams. 

C.C. 

Grams. 

Per  Cent. 

I . 

. . .2000 

.13848 

39-8 

•1393 

69.65 

2 . 

. . .3000 

.20772 

594 

.2079 

69.30 

3 * 

. . .4000 

.27696 

79-3 

.2775 

69.36 

4 • 

. . .2000 

.I3848 

39-6 

.1386 

6930 

The  theoretical  per  cent  of  acid  in  fused  borax  is  69.24. 
This  shows  that  this  method  is  a good  one,  applied  to 
borax.  The  next  thing  was  to  apply  it  to  tourmaline. 

A brown  tourmaline,  marked  (No.  2),  from  McAfifee, 
New  Jersey,  on  analysis  gave  the  following  : 


Silica 

Per  Cent. 

33-72 

Boric  acid  .... 

Alumina 

Ferric  oxide  . . . 

1.82 

Ferrous  oxide  . . 

323 

Lime 

Magnesia  .... 

14.07 

Loss  on  ignition  . . 

Potassium  oxide  . . 

20 

Sodium  oxide  . . . 

In  this  instance,  the  boric  acid  was  estimated  according 
to  Marignac’s  method. 

This  tourmaline  was  fused  with  potassium  and  sodium 
carbonates  : the  fusion  was  taken  up  with  water,  evaporated 
almost  to  dryness,  then  transferred  to  the  distilling  bulb 
together  with  the  insoluble  oxides.  The  distilling  bulb 


24 


instead  of  resting  on  an  asbestos  pad,  was  immersed  to 
half  the  depth  of  the  bulb,  in  a glycerine  bath.  The  tem- 
perature of  the  bath  was  raised  to  135?  C.  and  the  contents 
of  the  flask  rapidly  evaporated  to  dryness  by  the  aid  of  a 
current  of  air.  This  required  about  an  hour.  The  glyce- 
rine bath  was  allowed  to  cool  down  to  50°  C.  and  a flask 
containing  sodium  hydrate  was  substituted  for  the  one  pre- 
viously used  to  catch  the  distillate.  The  contents  of  the 
bulb  were  made  decidedly  acid  and  the  distillation  with 
methyl  alcohol  commenced.  The  remainder  of  the  opera- 
tion was  the  same  as  with  borax. 

The  following  table  shows  the  results  oi  this  method : 


Weight  of  Mineral  (No.  2). 

N 

— NaOH. 

10 

B2O3. 

>.  Grams. 

C.C. 

Grams. 

Per  Cent. 

Ol 

O 

O 

O 

16.0 

.0560 

( I 1.20) 

5000 

16.0 

.O56O 

(ll.20) 

31.0 

VO 

00 

O 

(10.85) 

I. OOOO 

22.4 

.0784 

(7-84) 

I. OOOO 

27.4 

.0959 

9-59 

5000 

I3.6 

.0476 

9.52 

5000 

137 

•04795 

9-59 

In  numbers  5,  6 and  7,  the  fusion  was  allowed  to  cool 
completely  and  by  rolling  the  crucible  between  the  fingers 
with  gentle  pressure,  the  fusion  dropped  out.  It  was  placed 
in  the  distilling  flask,  the  crucible  rinsed  with  sul- 
phuric acid  (1  : 1)  and  the  washings  added.  Sulphuric 
acid  and  water  sufficient  to  break  the  mass  up  into  a mushy 
state,  were  poured  over  it  and  the  distillation  with  methyl 
alcohol  conducted  as  with  the  others. 

By  the  procedure  used  in  these  latter  determinations, 
the  entire  time  consumed  was  about  five  hours. 

A black  tourmaline  which  gave  according  to  Marignac’s 
method  9.87  per  cent  of  boric  acid,  treated  as  the  above 
gave  the  following : 


25 

Weight  of  Mineral. 

— NaOH. 
2 

B203. 

No.  Grams. 

c.c. 

Grams. 

Per  Cent. 

i 5coo 

2.9 

.05075 

10.15 

o 

o 

o 

1-0 

2.9 

.05075 

10.15 

From  datolite,  the  following  percentages  were 

obtained  : 

Weight  of  Mineral. 

F NaOH 

2 

B2O3. 

No.  Grams. 

iC.C 

Grams. 

Per  Cent. 

I 5000 

5.50 

.O9625 

19.25 

2 5000 

5*55 

.097125 

1943 

Another  sample  of  a 

brown 

tourmaline  marked  (No.  4) 

gave  these  results  : 

Weight  of  Mineral. 

? NaOH 

2 

B2O3. 

No.  Grams. 

c.c. 

Grams. 

Per  Cent. 

I . . . .5000 

2.80 

.O49O 

9.80 

2 . . . .5OOO 

2.90 

.05075 

10.15 

3 * • • -5000 

2.85 

.04988 

9976 

4 . . . 1. 0000 

5.70 

.09975 

9-975 

In  each  of  the  preceding  determinations  the  residue  in 
the  distilling  bulb  was  tested  for  boric  acid,  but  none  was 
found. 

These  results  show  this  to  be  a good  method  of  estimating 
boric  acid  wherever  it  is  associated  with  silica  and  alumina. 
The  time  consumed  is  considerably  less  than  that  required 
by  other  methods,  and  the  complete  isolation  of  the  boric 
acid  is  accomplished.  The  construction  of  the  apparatus 
required  by  this  method  is  an  objection,  a very  slight  one, 
however. 

It  occurred  to  me  that  possibly  a more  simple  method 
might  be  found  in  that  proposed  by  Smith  in  the  Am . 
Chew.  Jour.,  Vol.^,p.2yg.  With  this  in  view  I took  up 
the  method  of  Smith  for  investigation. 


26 


Estimation  of  Boric  Acid  by  the  Method  of  Smith. 

A borax  solution,  I c.  c.  of  which  contained  .004  gram 
of  Na2B407,  a potassium  permanganate  solution  containing 
zinc  sulphate,  1 c.c.  of  which  was  equivalent  to  .0018705 
gram  of  manganese,  and  a manganous  sulphate  solution 
containing  .005228  gram  of  manganese  in  each  c.  c.,  were 
prepared.  To  a volume  of  the  manganous  sulphate  solu- 
tion, a known  portion  of  the  borax  solution,  with  an  equal 
quantity  of  alcohol,  was  added.  As  soon  as  the  precipitate 
settled  it  was  filtered  off  by  means  of  a Gooch  crucible  and 
a suction  pump.  The  filtrate  containing  the  excess  of  man- 
ganous sulphate  was  evaporated  to  dryness,  the  residue  gen- 
tly ignited  and  when  cool  dissolved  in  water.  A few  drops  of 
a saturated  solution  of  sulphur  dioxide  were  added  to  aid 
in  dissolving  the  residue.  The  liquid  was  then  transferred 
to  a flask  and  brought  to  boiling.  The  titration  of  the 
manganese  according  to  Volhard’s  method  was  now  made, 
and  from  this  the  boric  acid  calculated  by  the  reaction 
MnS04  + Na2B407  = MnB407  + Na2S04. 


Borax 

Sol. 

Grm.  of 

MnS04 

Sol. 

Grm.  of 

C.  C.  of 

Excess 

Per  cent 

Vol. 
of  Al. 

No. 

C.  C. 

Borax . 

c.  c. 

Mn. 

KM11O4. 

of  Mn. 

b2o3. 

C.  C 

I . 

. . IO 

.04 

5 

.02614 

8.0 

.OI4964 

71.03 

15 

2 . 

. . IO 

.04 

5 

.92614 

8.0 

.OI4964 

71-03 

15 

3 • 

. . IO 

.04 

5 

.02614 

8.2 

•015338 

68.33 

IO 

4 . 

. . IO 

.04 

10 

.05228 

22.1 

•041338 

68.9I 

IO 

5 • 

. . 15 

.06 

10 

.05228 

18.9 

•035354 

71.71 

15 

6 . 

. . 15 

.06 

10 

.05228 

19.2 

•0359H 

69.38 

15 

7 • 

. . 25 

.10 

15 

.O7842 

27-3 

.05  IO65 

69.54 

20 

8 . 

. . 25 

.10 

15 

.O7842 

27-3 

.051065 

69.54 

20 

9 • 

. . 25 

.10 

25 

.13071 

55-3 

.10344 

69.30 

25 

10  . 

. . 20 

.08 

20 

.10456 

43-5 

. . . 

(67.68) 

20 

The  precipitate  of  Mn0,2B203  was  dissolved  off  the  filter 
by  a warm  aqueous  solution  of  sulphur  dioxide,  transferred 
to  a flask,  brought  to  boiling  and  the  manganese  then 


27 


titrated  with  permanganate  of  potash  according  to  the 
method  of  Volhard.  This  was  done  with  each  precipitate 
with  the  following  results  : 


No. 

KM11O4. 

c.  c. 

Grams  Mn 
with  2B2O3. 

Per  Cent 

b2o3. 

Total  Mn 
determined. 

Difference  from 
amount  taken. 

I . . 

. 6.0 

.011223 

7*- 

.026187 

.000046  plus. 

2 . . 

. 6.0 

.011223 

7I-3I 

.026l87 

.000046  plus. 

3 • • 

. 5<8 

.OIO849 

68.94 

.026187 

.000046  plus. 

4 • • 

. 5.9 

.OIIO36 

70.1 1 

.052374 

.00005  2 plus. 

5 • • 

. 9.0 

.OI6834 

7i.3i 

.052188 

.000094  minus. 

6 . . 

. 9.0 

.OI6834 

7i.3i 

.052188 

.000466  plus. 

7 • • 

. 14.5 

.027122 

68.94 

.O78187 

.000236  minus. 

8 . . 

• 147 

.O27496 

69.89 

.O78561 

.000138  plus. 

9 • • 

. 14.6 

.027310 

69.41 

0 

<-n 

0 

.000045  plus. 

10  . . 

. 15.0 

.028057 

7I-31 

. . . 

. . . 

This  shows 

that  boric  acid  in  borax  may 

be  successfully 

estimated  either  by  the  titration  of  the  excess  of  manganous 
sulphate,  which  is  Smith’s  method,  or  by  titration  of  the 
manganese  combined  with  B203. 

For  the  estimation  of  boric  acid  in  a tourmaline,  Smith 
digested  the  extract  of  the  sodium  carbonate  fusion  with 
an  amount  of  ammonium  sulphate  equivalent  to  the  car- 
bonate. The  precipitate  that  formed  was  removed  and  the 
filtrate  concentrated  to  25  c.  c.,  after  which  it  was  treated 
as  the  borax  solution.  This  I did,  but  upon  adding,  the 
manganous  sulphate  obtained  no  precipitate,  and  upon  test- 
ing with  litmus,  found  the  liquid  acid.  This  corroborates 
Bodewig’s  statement  in  the  Zeit.fur  analyt.  Chemie}  Vol.  23, 
p.  14.3.  Another  fusion  was  made  and  the  extract  evapor- 
ated to  a volume  of  20  c.  c.,  then  transferred  to  a flask 
connected  with  a reflux  condenser,  and  digested  with  am- 
monium sulphate.  The  precipitate  was  removed  and  the 
filtrate  and  washings  concentrated  to  a volume  of  25  c.  c. 
To  the  solution,  which  was  faintly  ammoniacal,  a known 
volume  of  manganese  sulphate,  with  an  equal  volume  of 


28 


alcohol,  was  added.  As  soon  as  the  precipitate  had  settled 
it  was  filtered  off  and  washed  with  alcohol  and  water  (one 
to  one).  The  filtrate  was  evaporated  to  dryness  and  the 
residue  ignited ; when  cool,  it  was  taken  up  with  water  and 
a drop  of  aqueous  sulphur  dioxide  added.  The  liquid  was 
brought  to  boiling  and  the  manganese  titrated  with  potas- 
sium permanganate.  Two  determinations  gave  respectively 
23  per  cent  and  28.12  per  cent  of  boric  acid. 

There  is  no  doubt  but  that  in  the  ammoniacal  solution 
manganic  hydrate  is  formed  and  carried  down  with  the 
manganese  borate.  I dissolved  this  precipitate  in  aqueous 
sulphur  dioxide,  and  attempted  to  remove  the  manganese 
from  the  boron  trioxide,  in  order  to  titrate  the  B203  with 
sodium  hydrate,  but  could  find  no  means  of  separating  the 
two  without  volatilizing  some  boric  acid  or  introducing 
harmful  reagents. 

My  attention  was  next  turned  towards  the  method  used 
by  Honig  and  Spitz  (Zeit.  fur  angewandte  Chemie  1896,551), 
for  the  determination  of  boric  acid  in  a “ Gasgliihlichtcyl- 
inder,”  with  the  hope  of  obtaining  a simple  method  appli- 
cable to  tourmaline. 

The  Honig  and  Spitz  Method  of  Determining  Boric 
Acid  in  Insoluble  Silicates. 

The  extract  of  the  fusion  of  a brown  tourmaline  was 
digested  with  an  amount  of  ammonium  chloride,  equivalent 
to  the  carbonate  used  in  the  fusion,  and  the  precipitated 
alumina  and  silica  filtered  off.  An  ammoniacal  zinc  oxide 
solution  was  added,  and  the  whole  boiled  until  all  the  am- 
monia was  expelled.  The  zinc  oxide,  with  any  silica  it 
carried,  was  removed  and  the  filtrate  concentrated  to  a small 
volume.  After  being  made  slightly  acid  with  hydrochloric 
acid,  the  solution  was  boiled  for  fifteen  minutes  in  a flask 
connected  with  a reflux  condenser ; when  cooled  the 


29 


condenser  was  washed  out  with  water  (the  washings  going 
into  the  flask),  and  after  neutralizing  the  excess  of  hydro- 
chloric acid,  the  titration  for  boric  acid  was  made. 

The  results  obtained  were  very  high,  and  in  every  in- 
stance after  titration,  a white  precipitate  which  proved  to  be 
alumina  and  zinc  oxide,  separated.  This  further  shows  that 
boric  acid  cannot  be  separated  from  alumina  by  digestion 
with  ammonium  salts  and  that  the  removal  of  zinc  oxide 
by  this  means  is  a difficult  task. 

The  following  course  was  then  pursued.  After  the  addi- 
tion of  ammonium  chloride,  the  extract  of  the  fusion  was 
evaporated  to  dryness,  the  residue  gently  ignited  to  expel 
the  ammonium  chloride  and  when  cool,  taken  up  with 
water.  Any  insoluble  matter  was  removed,  a small  amount 
of  sodium  carbonate  added  and  the  whole  boiled  for  a few 
minutes.  When  cool,  the  carbon  dioxide  was  expelled  by 
adding  hydrochloric  acid  and  boiling,  and  the  boric  acid 
titrated  after  neutralizing  the  excess  of  hydrochloric  acid. 
Tenth  normal  sodium  hydrate  was  used  with  the  following 
results : 


Weight  of  Mineral  (No.  2). 

^NaOH 

IO 

b2o3 

Grams. 

c.c. 

Grams. 

Per  Cent. 

. . .2000 

4-5 

.01575 

7-875 

. . .5000 

10.5 

•03675 

7-35 

. . .5000 

1 1.2 

.0392 

7.84 

These  results  are  lower  than  those  previously  obtained  in 
the  same  sample  (page  24),  and  are  due  to  the  volatilization 
of  some  of  the  boric  acid  during  the  ignition  necessary  to 
completely  expel  the  ammonium  salts,  and  it  may  be  that 
some  of  the  acid  is  lost  in  the  boiling  with  the  ammonium 
salt.  In  commenting  on  the  method  of  Smith,  Bodewig 
(Zeit.fur  analyt.  Chentie  1884,  14.3)  says  that  some  of  the 
boric  acid  resulting  from  the  decomposition  of  the  borax 
by  the  ammonium  salt,  would  be  volatilized  in  the  boiling; 


30 


upon  testing  the  escaping  vapor,  he  found  it  alkaline,  while 
the  solution  at  the  same  time  was  acid. 

To  determine  just  how  much  boric  acid  was  volatilized 
in  this  way,  I decomposed  a solution  200  c.c.  in  volume, 
containing  1 gram  of  Na2B407,  by  distilling  with  ammonium 
chloride;  the  solution  was  distilled  to  one-fourth  its  vol- 
ume. The  distillate  contained  .02275  gram  of  B203,  equiva- 
lent to  2.275  Per  cent  of  the  borax  or  3.29  per  cent  of  the 
total  boric  acid.  This  shows  the  necessity  of  avoiding  the 
boiling  of  an  ammoniacal  boric  acid  solution. 

The  digestion  with  ammonium  chloride,  using  a reflux 
condenser  to  prevent  the  loss  of  boric  acid,  was  tried,  but  it 
was  impossible  to  get  rid  of  the  silica,  alumina  and  ammo- 
nium salt  in  this  manner.  Evaporation  to  dryness  and 
ignition  seemed  to  be  the  only  way  to  make  the  silica  and 
alumina  insoluble  and  destroy  the  ammonium  salt. 

The  Use  of  Lime  to  Prevent  the  Volatilization  of 
Boric  Acid  During  Evaporation. 

It  occurred  to  me  that  the  loss  of  boric  acid  during  the 
evaporation  to  dryness  and  subsequent  ignition,  might  be 
avoided  by  the  addition  of  lime.  Therefore,  after  digesting 
the  extract  of  the  fusion  with  ammonium  chloride  in  a flask 
connected  with  a reflux  condenser,  and  removing  the  pre- 
cipitate, I added  lime  obtained  by  the  ignition  of  precipitated 
calcium  carbonate,  and  evaporated  the  whole  to  dryness  in 
a platinum  dish  and  ignited  strongly.  Soda  in  excess  of 
the  amount  required  by  the  lime,  and  25  c.c.  of  water  were 
added  and  the  whole  digested  for  half  an  hour.  When 
cool,  the  precipitate  was  removed  and  well  washed  with 
cold  water.  After  concentrating  the  filtrate  and  allowing  it 
to  cool,  sulphuric  acid  was  carefully  added  to  almost  the 
neutral  point ; the  precipitate  that  formed  was  filtered  out 
and  the  solution  made  just  acid  and  the  boric  acid  then 
titrated.  The  following  table  shows  the  results  obtained 


3i 


from  the  brown  tourmaline  (No.  4),  which  according  to  the 
previous  method  (page  25)  contained  9.97  per  cent  of  boric 
acid  : 


Weight  of  Mineral  (No.  4). 

N 

— NaOH. 

2 

Bg03. 

No 

Grams. 

C.C. 

Grams. 

Per  Cent. 

I • 

. . .5000 

2.9 

.05075 

IO  15 

2 

. . .5000 

30 

.0525 

10.50 

3 • 

. . .3OOO 

1.6 

.0280 

933 

4 • 

.3000 

i-75 

.03062 

10.21 

In  these  determinations  the  insoluble  oxides  were  refused 
and  the  extract  of  the  fusion  added  to  that  of  the  first. 

To  ascertain  whether  the  CaO,B203,  formed  upon  the 
addition  of  lime  to  the  ammoniacal  boric  acid  solution,  was 
completely  decomposed  by  the  boiling  with  sodium  car- 
bonate, a weighed  amount  of  borax  was  subjected  to  the 
same  treatment  as  the  extract  of  the  fusion.  That  the 
C l0,B203  was  entirely  decomposed  by  the  boiling  with 
soda,  is  proven  by  this  table. 


Taken. 

Found. 

Vol.  Weight  of 

of  Sol.  Borax. 

b,o3. 

N 

- NaOH. 

2 

b3o3. 

No. 

C.C.  Grams. 

Grams. 

C.C. 

Grams. 

I . . 

. 10  .01 

.OO6924 

04 

0.007 

2 . . 

. 10  .01 

.OO6924 

O.4 

0007 

3 • • 

. 20  .02 

.013848 

0.8 

0.014 

A black  tourmaline,  in  which,  as 

previously  shown,  the 

boric 

acid  amounted  to 

10.15  Per 

cent,  yielded  9.92  per 

cent  when  subjected  to  the  above  treatment. 

Datolite  gave  the  following  : 

Weight  of  Mineral. 

N 

— NaOH. 

2 

Bi03. 

No. 

Grams. 

C.C. 

Grams. 

Per  cent. 

1 . . 

. . . .5000 

54 

.0945 

1 8.90 

2 . . 

. . . .3000 

3-3 

•05775 

19.25 

32 


This  same  datolite,  according  to  the  method  on  page  25, 
contained  19.25  per  cent  of  boric  acid. 

By  using  barium  hydrate  in  place  of  the  lime  and  sodium 
sulphate  instead  of  the  carbonate,  the  following  results 
were  obtained  from  the  brown  tourmaline  (No.  4)  : 


Weight  of 
Mineral. 

— NaOH. 

£ 

BgOj. 

).  Grams. 

C.C 

Grams, 

Per  cent. 

3000 

1.3 

.02275 

7.58 

3000 

1.8 

•0315 

10.50 

1.6 

.0280 

9-33 

2770 

1-5 

.02625 

949 

5000 

2.6 

.0455 

9 10 

5000 

2.4 

.0420 

8.40 

In  this  series,  the  insoluble  oxides  were  not  refused,  but 
were  dissolved  in  sulphuric  acid  and  subjected  to  distilla- 
tion with  methyl  alcohol,  etc.,  whereupon  the  following 
percentages  were  obtained : 

^NaOH.  bso3. 

2 


No.  C.C,  Grams.  Per  Cent. 

1  0.2  .0035  1. 16 

2  0.1  OOI75  O.58 

3  0.1  .00175  0.58 

4  005  .000875  0.29 

5  o i .00175  0.58 


Upon  igniting  the  distillate  of  number  6,  the  charac- 
teristic green  flame  of  boron  was  obtained.  If  these  per- 
centages are  added  to  those  previously  obtained,  it  will  be 
noticed  that  it  makes  the  boric  acid  found  in  numbers  3,  4 
and  5 respectively  9.92  per  cent,  9.80  per  cent  and  9.45  per 
cent.  These  numbers  agree  fairly  closely  with  those 
obtained  from  the  same  tourmaline  by  the  method  described 
on  page  25.  From  the  foregoing,  the  necessity  of  refusing 
the  insoluble  oxides  in  order  to  entirely  remove  the  boric 
acid  is  apparent. 


33 


This  method,  while  not  giving  results  as  reliable  as  that 
in  which  the  boric  acid  is  volatilized  as  the  methyl  ester,  yet 
answers  fairly  well  and  avoids  the  use  of  complicated 
apparatus : the  time  is  lessened  very  little  if  at  all.  If  the 
digestion  with  ammonium  chloride  could  be  avoided,  that  is 
if  the  alumina  could  be  separated  from  the  boric  acid  by 
some  other  means,  the  evaporation  to  dryness  and  ignition 
might  be  unnecessary  and  thus  the  time  shortened.  In 
looking  for  a means  of  accomplishing  this  object,  I hap- 
pened upon  the  reaction  2A10  0Na  -f-  C02  -f-  3H20  = 
AI2(OH)6  -f-  Na2C03  which  is  made  use  of  in  the  manufac- 
ture of  soda  from  cryolite.  Hoping  by  this  means  to 
separate  the  alumina  from  the  boric  acid,  I conducted 
carbon  dioxide  into  the  boiling  solution  of  the  sodium  car- 
bonate fusion  free  from  the  insoluble  oxides.  The  separa- 
tion, however,  was  not  complete,  as  the  following  show : 

Weight  of  Mineral.  *1  NaOH.  P203. 


2 

No.  Grams.  C.  C.  Grams.  Per  Cent. 

1  5000  12.0  .2100  42.00 

2 3000  100  -1/50  58.33 


The  solutions,  after  titration,  were  found  to  contain  large 
amounts  of  alumina. 

By  passing  carbon  dioxide  through  a cold  solution  of 
sodium  aluminate,  Day  (Am.  Chem.  Jour.,  Vol.  19,  p.  718) 
completely  separated  all  the  alumina  from  the  soda.  I then 
passed  carbon  dioxide  through  the  cold  fusion  extract,  as 


shown  in  this  table : 

Time  of  Conducting  C02 

Volume 

through  the  Sol. 

of  Sol. 

Hours. 

C.  C. 

2-5 

200 

a precipitate  formed1. 

2.0 

300 

<<  <<  a 

1.0 

350 

»<  «<  << 

2.0 

500 

no 

7.5  total  time.  Temp,  of  sol.  i°C. 


34 


The  solution  was  then  evaporated  to  a small  volume,  and 


after 

the  expulsion 

of  all  the  carbon 

dioxide,  titrated  for 

boric  acid. 

N 

Weight  of  Mineral  (No  4).  — . NaOH. 

2 

e2o3. 

No. 

Gram. 

c.  c. 

Gram. 

Per  Cent. 

I . . 

3000 

1.95 

•03413 

n-34 

After  titration,  upon  boiling  with  hydrochloric  acid  and 
adding  ammonia,  a precipitate  of  alumina  was  obtained 
which  weighed  .0039  gram,  equivalent  to  1.3  per  cent  of  the 
mineral. 

This  procedure  was  then  repeated  with  the  following 
results  : 


Time  of  Conducting  C02 

Volume 

through  the  Sol. 

of  Sol. 

Hours. 

C.  C. 

2.0 

300 

a precipitate 

4.6 

400 

a a 

1.0 

ROO 

no 

7.0  total  time.  Temp,  of  sol.,  i°  C. 


The 'treatment  was  as  in  the  former  case  and  12.77  per 
cent  of  boric  acid  was  found.  Upon  testing  the  titrated 
solution  for  alumina,  .0075  gram,  equivalent  to  1.5  per 
cent  of  the  mineral  was  obtained. 

In  all  attempts  to  determine  the  boric  acid  in  tourmalines 
containing  much  alumina  great  difficulty  has  been  experi- 
enced in  separating  the  alumina  from  the  boric  acid  and 
alkali  carbonate.  In  following  out  Marignac’s  method, 
alumina  is  always  found  with  the  magnesium  borate,  mag- 
nesium chloride  and  silica.  The  tenacity  with  which  boron 
oxide  and  alumina  hold  to  one  another  in  other  than  acid 
solutions  is  extremely  great,  as  has  already  been  demon- 
strated and  is  further  shown  by  the  following  experi- 
ment : 


35 


.1733  gram  of  aluminium,  corresponding  to  .32565  gram 
of  A1203,  was  dissolved  in  hydrochloric  acid  and  the  excess 
of  acid  expelled  ; 2.019  grams  of  fused  borax  and  1.0  gram 
of  sodium  carbonate  dissolved  in  water,  were  added  to  the 
aluminium  chloride  and  the  whole  boiled  one  hour.  These 
proportions  were  taken  from  the  equation  3ll20  + 3Na2B4 
07  -{-  A12C16  = Al2(OH)6  + 6NaCi  -f-  2B203.  The  precipi- 
tated alumina  was  well  washed,  dissolved  in  hydrochloric 
acid,  reprecipitated  by  ammonia,  ignited  and  weighed.  It 
equaled  .2906  gram,  or  89.23  per  cent  of  all  the  alumina 
present  in  the  solution.  The  washings,  after  boiling  to  expel 
the  ammonia,  were  added  to  the  filtrate.  The  volume  of 
the  solution  then  equaled  400  c.  c.,  and  when  cooled  to  i°  C. 
carbon  dioxide  was  conducted  through  it  for  fifteen  hours. 
The  precipitate  was  removed  and  treated  as  the  first ; it 
amounted  to  .0332  gram,  or  11  plus  per  cent  of  all  the 
alumina.  This  with  the  former  percentage  equals  10023 
per  cent.  Carbon  dioxide  passed  through  two  hours  longer 
caused  no  further  precipitation,  yet  upon  acidifying,  then 
adding  ammonia,  a precipitate  was  obtained  which  amounted 
to  .005 1 gram  of  A1203,  or  1.56  per  cent.  The  total  amount 
of  A1203  was  .32565  gram,  while  that  estimated  equaled 
.3289  gram.  This  excess  is  due  beyond  a doubt  to  the 
contamination  of  the  precipitates  with  boric  acid,  although 
in  all  except  this  last  instance  the  precipitates  were  dissolved 
in  hydrochloric  acid  and  reprecipitated  by  ammonia. 

The  obstinacy  with  which  A1203  and  B203  cling  together, 
it  seems  to  me,  would  indicate  the  existence  of  a salt  of 
aluminium  and  boron  in  this  alkaline  solution.  This  would 
also  favor  the  view  held  by  Clarke  ( Bulletin  125,  United 
States  Geological  Survey),  which  he  expresses  in  his 
structural  formula  for  tourmaline. 


Si04  = A1 

/ 

A'-Si04=Al 


Si04  ■=  A1-B02 
Al-BOg  = NaH 
s;o4  = A1-B02 


Al-Si04  = MgH 

\ 

Si04  = MgH 


boric  acid,  the  alumina 


The  alumina,  as  is  seen,  links 
the  boric  acid  to  the  silica.  This 
view,  I think,  is  further  strength- 
ened by  the  fact  that  calcium  or 
barium  carbonate  fused  with  borax, 
then  boiled  with  sodium  carbonate 
or  sulphate,  gave  up  all  the  B203 
to  the  alkali ; while  tourmaline, 
heated  with  calcium  or  barium 
carbonate,  then  boiled  with  car- 
bonate or  sulphate  of  soda,  yielded 
to  the  alkali  but  a portion  of  the 
most  likely  held  the  remainder. 


SUMMARY. 


In  order  to  avoid  the  introduction  of  alkalies,  which,  as 
it  has  been  shown,  are  objectionable,  new  methods  for  the 
decomposition  of  the  mineral  were  attempted.  The  first  of 
these  was  the  heating  of  the  mineral  with  metallic  mag- 
nesium and  subsequently  volatilizing  the  boron  by  heating 
in  a stream  of  chlorine.  From  all  appearances,  the  decom- 
position of  the  mineral  was  complete,  but  in  the  treatment 
with  chlorine,  either  the  boron  was  partially  retained  by 
the  other  chlorides  formed  at  the  same  time,  or  if  it  was 
entirely  volatilized  as  the  chloride,  it  was  not  decomposed 
when  it  came  in  contact  with  the  water  saturated  with  chlo- 
rine. By  using  a large  volume  of  water  this  difficulty 
might  be  avoided,  but  if  the  chlorine  is  removed  by  draw- 
ing air  through  the  solution,  some  boric  acid  would  be 
carried  out  with  it.  Again,  if  alkali  is  added,  hypochlorite 
of  the  alkali  would  be  formed,  and  this,  when  neutralized, 
would  free  chlorine,  which  again  would  likely  carry  with  it 
boric  acid,  or  the  hypochlorous  acid  formed  would  cause 
trouble  in  the  titration. 


37 

By  fusing  the  mineral  with  calcium  carbonate,  also  with 
barium  carbonate,  a complete  decomposition  was  obtained, 
but  the  separation  of  the  boric  acid  was  incomplete.  Some 
of  the  boric  acid  was  held  by  the  alumina,  which  was  refused 
to  yield  it  to  the  alkali  with  which  the  fusion  was  digested. 
This  must  be  the  case,  since  calcium  or  barium  carbonate 
fused  with  borax,  then  boiled  with  sodium  carbonate  or 
sulphate,  gave  up  all  the  B203.  This  strengthens  the  idea 
that  the  boron,  which  is  so  constant  a quantity  in  tourma- 
lines, is  linked  through  the  aluminium  to  the  silica,  prob- 
ably as  an  aluminium  metaborate,  as  Clarke  suggests. 

The  mineral  was  then  fused  with  alkali  carbonates,  and 
by  volatilizing  the  boron  from  an  acid  solution  as  the  methyl 
ester,  the  boron  was  successfully  isolated  and  its  estimation 
made  by  the  volumetric  method  of  Thompson.  The  use 
of  a current  of  air  with  the  apparatus  described,  shortens 
the  time  required  for  the  volatilization  of  the  ester,  very 
materially.  As  has  been  shown,  impure  methyl  alcohol 
prevents  the  complete  volatilization  of  the  boric  acid.  The 
results  obtained  by  this  method  are  reliable,  and  the  method 
is  capable  of  very  wide  application.  The  great  affinity  that 
alumina  has  for  boric  acid,  has  been  pretty  thoroughly 
demonstrated  in  the  foregoing  work,  and  the  most  successful 
means  of  overcoming  this  affinity  and  completely  separating 
these  two,  is  by  volatilizing  the  boric  acid  from  an  acid 
solution.  If  an  acid  or  ammoniacal  borax  solution  is  boiled, 
there  is  the  likelihood  of  a very  appreciable  loss  of  boric 
acid : by  this  method  there  is  no  boiling  of  acid  or  ammo- 
niacal solutions.  These  facts,  and  the  brief  time  required 
for  its  performance,  recommend  this  method  for  the  estima- 
tion of  boric  acid  in  all  silicates. 

Could  boric  acid  be  separated  from  manganese,  without 
volatilization,  its  estimation  in  silicates  could  be  accom- 
plished through  the  salt  MnO,2B2Os.  As  has  already  been 
proven,  the  method  is  successful  when  applied  to  borax. 


38 


If  the  attempt  is  made  to  remove  the  manganese  with 
alkali,  the  precipitation  is  incomplete;  if  ammonium  sul- 
phide is  used,  the  difficulties  encountered  are  well  known, 
and  if  the  manganese  is  precipitated  from  an  acid  solution, 
boric  acid  is  volatilized. 

As  has  been  shown,  the  volatility  of  boric  acid  in  am- 
monia is  very  appreciable,  hence  any  method  in  which  an 
ammoniacal  boric  acid  solution  is  boiled  in  the  open,  is 
unreliable,  unless  some  substance  is  introduced  to  bind  the 
acid.  I have  used  lime  for  this  purpose,  and  found  it  to 
fulfill  its  end. 

By  refusing  the  insoluble  oxides  with  alkali  carbonate,  it 
is  possible  to  separate  the  boric  acid.  However,  I do  not 
believe  the  separation  is  complete  even  then,  but  that  the 
amount  of  boric  acid  left  after  the  first  fusion  is  so  diluted 
by  the  second,  that  what  remains  with  the  insoluble  oxides 
may  be  neglected.  By  twice  fusing  and  digesting  the 
extract  with  ammonium  chloride  with  a reflux  condenser, 
then  evaporating  the  solution  to  dryness  with  lime  in  a 
platinum  dish  and  igniting  the  residue,  the  silica  and  alum- 
ina are  made  insoluble ; then  digestion  with  sodium  car- 
bonate gives  borax  in  which  the  boric  acid  is  readily  titrated 
by  the  method  of  Thompson.  This  method  works  very 
well  with  alumina  containing  silicates ; with  datolite,  better 
results  were  obtained.  It  avoids  the  use  of  complicated 
apparatus  and  requires  for  its  execution  about  four  hours. 
With  silicates  decomposable  by  digestion  with  acids 
( Wohler , Cliem.  News , i86j}  255,  and  Handb.  der  Mineral, 
Analyse , under  Datholite ),  it  seems  to  me,  this  would  be  the 
method. 

The  obstinacy  that  is  encountered  in  separating  alumina 
from  B2Os  in  an  alkaline  solution,  calls  to  my  mind  a point 
which  I think  is  worthy  of  some  attention.  In  the  com- 
plete analysis  of  minerals,  such  as  tourmaline,  it  is  cus- 
tomary to  evaporate  the  hydrochloric  acid  solution  of  the 


39 


fusion  to  dryness,  remove  the  silica  and  precipitate  the  iron 
and  alumina  from  the  filtrate  as  hydrates  by  ammonia. 
Although  these  hydrates  have  been  dissolved  in  hydro- 
chloric acid  and  reprecipitated,  yet  considerable  difficulty  is 
experienced  in  obtaining  two  determinations  from  the  same 
sample  that  agree.  This  trouble  I believe  to  be  due  to  boric 
acid,  which  does  not  go  off  in  the  evaporation  to  dryness 
with  hydrochloric  acid.  If  this  be  true,  by  the  addition  ot 
methyl  alcohol  during  the  evaporation  with  hydrochloric 
acid,  this  difficulty  might  be  eliminated. 

The  facts  to  which  I have  called  attention  in  the  latter 
part  of  this  paper,  argue  strongly  for  the  formula  proposed 
by  Clarke  to  represent  the  structure  of  tourmaline.  But,  as 
I have  said,  we  know  nothing  of  the  magnitude  of  the  mole- 
cule, hence  such  representations  are  surmises  only.  Until 
some  means  of  ascertaining  the  size  of  the  mineral  molecule 
has  been  devised,  such  formulas  will  have  to  be  looked 
upon  with  doubt. 


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